I've endlessly searched the web and this forum to try and diagnose my issue -- 97 XJ 4.0L AW4 2WD 73K…I’m completely stumped on my CEL/ rough chugging idle (most noticeably when cold, but always comes back when at operating temperature). Didn’t do this before as I drove it for about 2000 miles after purchasing it. I’m 2nd owner. The XJ was in like new condition, but I did a few mods…Borla header & cat back exhaust, Magnaflow cat, all new Mopar sensors – IAC, TPS, MAP, CPS, pre & post oxygen sensors; new ignition coil (Mopar), new Denso distributor wires, Champion 4122 spark plugs, ’00 XJ intake manifold. Has no power when cold, stumbling badly. Get P105 code repeatedly, and then when push it onto freeway get P206 & P305 (cylinder 5 & 6 misfires). Swapped out the oxygen and MAP sensors again just in case they were bad out of the box. I wired in a factory ‘extened idle’ switch and believe I had the positive and negative in the wrong spot and that kicked on a CEL – maybe I had damaged the PCM? No clue. Any experience with issues like this/ causes/ fixes?? Help… I’m down to bad PCM, bad wiring same where in the engine harness, and/or possibly the newer intake manifold? I've also checked all the vacuum caps/ lines for cracks and nada. All solid. Any advise is appreciated. Thanks

 

My poor idle problems have been remedied by replacing IAC and/or the front O2 sensor.

You bought it, drove it for 2000 miles and it ran fine. Why did you start throwing new parts on it and, moreover, why the extended idle switch? Just curious.

https://wranglertjforum.com/threads/...ower-gains.49/





'99-Up Horseshoe Intake
Myth: According to that great wealth of information that is never wrong, the Internet says you'll get a 5-30hp gain thanks to the '99-up 4.0L's swooped, equal length runners and larger plenum volume.

Our Thoughts: While a free-flow intake manifold can deliver more power, it's only going to allow as much air to flow as the cylinder head and camshaft will call for. Upping the intake runner volume too much will cause the intake charge to lose velocity, killing low- and mid-speed power and torque. On a '98-earlier engine running a stock camshaft and unported cylinder head, it's wasted effort.

Claimed Gains: 5-30hp
Actual Gains: 5hp loss on Trasborg's '98 XJ (Project Mileage Master)